1. Field of the Invention
The present invention relates to a process for producing a ceramic substrate, and more particularly, to a ceramic substrate production process for producing a ceramic substrate having a step portion on at least one principal surface thereof, and also to a ceramic substrate produced by using the process.
2. Description of the Related Art
Ceramic substrates having step portions (typically, a cavity) provided on the surfaces thereof are known.
A process has been proposed in Japanese Unexamined Patent Application Publication No. 3-169097 for producing this type of ceramic substrate in which, as shown in FIGS. 26A, 26B, and 26C, a multilayered ceramic substrate having a step portion (cavity) is produced by superposing second ceramic sheets 52, each having an opening portion 53, on first ceramic sheets 51, followed by press-bonding, to thereby form a laminate structure 57. In this process, a plate member 54 (including a ceramic sheet 56 and another ceramic sheet 56 with a releasing agent 55) having a shape that is substantially identical to that of the opening portion 53 is placed in the opening portion 53 so that a surface 54a is slightly protruded from the surface of the laminate structure 57, and, after a subsequent press-bonding, the plate member 54 is removed, so that a desired cavity 58 is formed with a high degree of dimensional precision.
This process, however, requires laborious work for punching ceramic sheets and, in addition, a complicated process for performing press-bonding to be conducted prior to firing, resulting in an increased production cost. Another problem is that it is not easy to maintain the required degree of dimensional precision due to influence of undulation encountered in the course of firing.